The present invention relates to a high-voltage circuit breaker having two arcing contacts arranged coaxially relative to one another and having an insulating nozzle which surrounds a contact gap between the arcing contacts at least during an opening operation. The nozzle has a through-channel that in the closed state is blocked by the first of the arcing contacts which has a shaft and an end element having a smaller diameter than that of the shaft.
A high-voltage circuit breaker is described in U.S. Pat. No. 4,342,890. In this switch, in the event of an opening operation, the arcing contacts are separated from one another in the axial direction, whereupon in many instances an arc is formed between them in the contact gap. The extinguishing gas that is present, usually SF6, is heated up by this arc and flows into a heating area where it is stored temporarily. From there, when the current passes through zero and the arc is thus extinguished, the extinguishing gas, which is at high pressure, passes into the arc area and thus to the contact gap so as to cool it and prevent restriking. The insulating nozzle is provided in order to direct the flow of extinguishing gas, and to accelerate and control the flow of extinguishing gas. In particular, the through-channel of the insulating nozzle remains closed off by an arcing contact until the extinguishing position is reached, so that initially the pressure of the extinguishing gas can increase in the contact gap, and as a result the gas flows more rapidly once the through-channel is opened up.
In the space between the arcing contact that temporarily blocks the through-channel and the material of the insulating nozzle, dielectric problems may arise due to the strong field intensity there. An end element of the arcing contact may be designed so that its diameter is smaller than that of the shaft, so that during the time period when the arcing contact opens the through-channel there is a gas gap between the end element of the arcing contact and the wall of the through-channel that thus prevents or reduces the dielectric problems.
One problem associated with this is that in a gap of this kind extinguishing gas can escape prematurely from the contact gap and is therefore no longer available to help cool the contact gap subsequently.
An object of the present invention is to create a high-voltage circuit breaker of the aforementioned kind in which, when the insulating nozzle is opened up by the arcing contact, as much extinguishing gas as possible is available in the area of the contact gap, and in which one can ensure dielectric strength in the area between the end element of the arcing contact and the material of the insulating nozzle.
According to an example embodiment of the present invention, this object is achieved in that the through-channel has a cylindrical part whose diameter is only slightly greater than the diameter of the shaft.
The design according to the present invention ensures that the through-channel remains largely closed off until it is opened by the shaft of the first arcing contact, and also ensures that once the through-channel has been opened up, the end element of the arcing contact is separated from the material of the insulating nozzle by enough of a gap so that the dielectric load in the space between the first arcing contact and the material of the insulating nozzle is reduced.
This also ensures that the through-channel is sealed effectively by the first arcing contact during the period when the shaft blocks the cylindrical part of the through-channel. For tolerance-related reasons, and to ensure the arcing contact can move freely, there is a small gap between the outside diameter of the shaft and the wall of the through-channel; however, this gap is small enough to ensure that little extinguishing gas escapes, in particular because at least at the beginning of an opening operation the through-channel is blocked along a considerable length so that the extinguishing gas has to flow through the gap along a considerable length in order to reach an expansion area. In practice this cannot be achieved using a conventional nozzle having a local narrow point.
According to an example embodiment of the present invention, the length of the end element is greater than the length of the cylindrical part.
According to a further example embodiment of the present invention, the length of the cylindrical part is greater than its diameter, in particular greater than twice the diameter. It is also advantageous if the length is greater than three times or four times the diameter of the cylindrical part.
The length ratios of the end element and the cylindrical part ensure that at the point in time when the free end of the end element is pulled back into the through-channel and the dielectric load between this free end and the wall of the through-channel is particularly great, the shaft has already opened up the through-channel. As a result, gas starts to flow at this point in time and thus prevents flashover at the free end of the end element.
Particularly if the cylindrical part is long, the resistance to flow is considerable thanks to the fact that the gap between the shaft and the wall of the through-channel is narrow, thus ensuring an effective seal.
The through-channel is not opened up until the contact pin has travelled a significant distance, so that substantial extinguishing gas pressure can build up in the heating area and, respectively, compression area over a long period of time before the extinguishing gas starts to flow.
According to a further advantageous embodiment of the present invention, a conical transitional area is provided between the end element and the shaft of the first arcing contact.
Furthermore, it is advantageous if the through-channel has a conical extension on the end of the cylindrical part that faces away from the second arcing contact.